Synthetic lubricating composition



United States Patent 3,476,685 SYNTHETIC LUBRICATING COMPOSITION Frederick G. Oberender, Wappingers Falls, and Arthur W. Godfrey and Morris A. Wiley, Fishkill, N.Y., assignors to Texaco Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed May 8, 1967, Ser. No. 636,620 Int. Cl. Cm 3/20, 3/38 US. Cl. 252-46.7 13 Claims ABSTRACT OF THE DISCLOSURE A synthetic lubricating oil composition is disclosed comprising a major portion of an ester-base having lubricating properties formed by the reaction of a pentaerythritol or trimethylolpropane and an organic acid having from about 2. to 12 carbon atoms per molecule containing in combination a hydrocarbyl-substituted phosphoramidate, an alkylated arylamine and an alkylated phenothiazine.

This invention relates to a synthetic lubricating oil composition designed for the lubrication of turbine engines. More particularly, the invention relates to an esterbase lubricating oil composition having outstanding oxidation and corrosion resistance and deposit-inhibiting properties.

Aircraft turbine engines must be capable of operating over a wide temperature range under severe operating conditions. Synthetic lubricants of the ester-base type have been found to be useful in meeting the lubricating requirements of todays high performance turboprop, turbojet, and turbofan engines. The natural properties of the synthetic base augmented by selected additive components provide a lubricant meeting the severe engine performance requirements of both military and commercial aircraft engine manufacturers. However, higher performance requirements are being set for the next generation of turbine engines and present day synthetic lubricants do not have the properties considered necessary to Withstand the substantially higher levels of thermal and oxidative stress imposed by these engines.

A novel ester-base lubricating oil composition has now been discovered which is effective to meet more stringent requirements of aircraft turbine engines.

The lubricating composition of this invention comprises the combination of an ester-base fluid having lubricating properties formed from the reaction of a pentaerythritol or trimethylolpropane and an organic acid having from about 2 to 12 carbon atoms per molecule containing from 0.1 to 4 percent of a phosphoramidate having the formula:

in which R is an aryl or alkaryl radical having from 6 to 20 carbon atoms and R and R" each represent a hydrocarbyl radical having from 4 to 20 carbon atoms, from about 0.5 to 4 percent of an alkylated diphenylamine in which the alkyl radicals have from 4 to 20 carbon atoms and from 0.1 to 3 percent of an alkylated phenothiazine in which the alkyl radicals have from 4 to 20 carbon atoms. The compounded lubricating oil of the invention can generally be further improved by adding minor amounts of conventional corrosion inhibitors.

The effectiveness of the lubricating oil of this invention is attributed to particular classes of synthetic base oils defined above together with a specific combination of additives. Criticality in the base oil is evidenced by the fact that diester type synthetic oil bases in lubricating oil formulations using the same additives do not provide an acceptable level of oxidation and corrosion resistance and cleanliness. Criticality with regard to the alkylated diphenylamine and alkylated phenothiazine components is evidenced by the fact that related or similar compounds as well as the absence of one or the other results in a lubriacting oil composition which fails to meet the required performance standards.

The base fluid component of the lubricant of the invention is an ester-base fluid prepared from pentaerythritol or trimethylolpropane and organic acids. Polypentaerythritols, such as dipentaerythritol and tripentaerythritol, can also be employed in the reaction to prepare the base oil.

The organic acids which are used to form the ester-base fluid include the straight-chain and branched-chain aliphatic acids, cycloaliphatic acids and aromatic acids as well as mixtures of these acids. The acids employed have from about 2 to 12 carbon atoms per molecule. Examples of suitable specific acids are acetic, propionic, butyric, valeric, isovaleric, caproic, pelargonic, decanoic, cyclohexanoic, naphthenic, benzoic acid, phenylacetic, tertiarybutylacetic acid and Z-ethylhexanoic acid.

In general, the acids are reacted in proportions leading to a completely esterified pentaerythritol or trimethylolpropane with the preferred ester bases being the pentaerythritol tetraesters. Examples of such commercially available tetraesters include pentaerythritol tetracaproate, which is prepared from purified pentaerythritol and crude caproic acid containing other C monobasic acids. Another suitable tetraester is prepared from a technical grade pentaerythritol and a mixture of acids comprising 38 percent valeric, 13 percent Z-methyl pentanoic, 32 percent octanoic and 17 percent pelargonic acids. Another effective ester is the triester of trimethylolpropane in which the trimethylolpropane is esterified with a monobasic acid mixture consisting of 2 percent valeric, 9 percent caproic, 13 percent heptanoic, 7 percent octanoic, 3 percent caprylic, percent pelargonic and 1 percent capric acids. Trimethylolpropane triheptanoate, trimethylolpropane pentanoate and trimethylolpropane hexanoate are also suitable ester bases.

The phosphoramidate component of the lubricant is represented by the formula:

in which R is an aryl or alkaryl radical having from 6 to 20 carbon atoms and R and R" each represent the same or a different hydrocarbyl radical having from 4 to 20 carbon atoms. R and R" can be alkyl cycloalkyl, aryl, alkaryl or aralkyl groups. The preferred phosphoramidates are those in which R, R' and R" each represent a phenyl or alkyl-substituted phenyl group. Phosphoramidates in which R is an alkyl radical appear to be unsuitable for this invention. Examples of effective phosphoramidate compounds are N-phenyl-0,0'-diphenylphosphoramidate, N dodecylphenyl 0,0" bis(octylphenyl)phosphoramidate, N-phenyl-0,0'-dioctylphosphoramidate, N-dodecylphenyl-0,0-bis (nonylphenyl)phosphoramidate, N nonin which R is an alkyl radical having from 4 to 20 carbon atoms and R is hydrogen or an alkyl radical having from 4 to 20 carbon atoms.

Examples of effective amines include dioctyldiphenylamine, dihexyldiphenylamine, decyldiphenylamine, didodecyldiphenylamine, octylphenyldecylphenylamine, hexylphenyl-ethylphenylamine, 2-ethylhexyldiphenylamine, and octyldiphenylamine. The preferred alkylated diphenylamines are those in which the alkyl radicals have from 8 to 12 carbon atoms. The alkylated diphenylamines disclosed appear to be critical in the compositions of the invention since other amine compounds do not provide the necessary properties to produce an effective lubricating oil composition. The alkylated diphenylamine is generally employed in a concentration ranging from about 0.5 to 4 percent with the preferred concentration being from about 0.7 to 2.5 percent.

An alkylated phenothiazine is also essential to lubricant of the invention. Effective alkylated phenothiazines correspond to the formula:

in which R is an alkyl radical having from 4 to 20 carbon atoms and R is hydrogen or an alkyl radical having from about 4 to 20 carbon atoms. Effective alkylated phenothiazines include di-tertiaryoctylphenothiazine, dibutylphenothiazine, 2-ethylhexylphenothiazine, butylphenothiazine, decylphenothiazine, dihexylphenothiazine and the like. The preferred alkylated phenothiazines are those in which the alkyl radicals have from 8 to 12 carbon atoms. Lubricating oil compositions containing phenothiazine instead of an alkylated phenothiazine exhibit an unsatisfactory level of deposit laydown and do not provide an acceptable lubricating oil composition in this respect. The alkylated phenothiazine is generally employed in a concentration ranging from about 0.1 to 3 weight percent with the preferred concentration ranging from 0.3 to 1 percent.

The phosphoramidate, alkylated diphenylamine and alkylated phenothiazine components of the lubricant of the invention are readily soluble in the ester-base in the percentage ranges disclosed. The lubricating oil composition can be prepared by adding the various components to the base oil in any order and mixing until a homogenous mixture is obtained.

It is conventional to employ other additives in a completely formulated synthetic lubricating oil composition. For example, methacrylate polymers are well known V.I. improvers and pour point depressants. While the ester-base lubricants possess good V.I. and pour properties, they nevertheless often require the presence of small concentrations of methacrylate polymers, or copolymers to improve dispersancy, or copolymers of alkylmethacrylates with vinyl monomers containing polar functional groups to meet the requirements of military specifications. These methacrylate polymers are often usually copolymers of two or more esters of methacrylic acid and usually have a molecular weight between 5000 and 20,000. The methacrylate esters have the following general forwherein R is an aliphatic radical having from about 4 to 18 carbon atoms. Copolymers which find particular use as V.I. improvers and pour point depressants are the following:

A copolymer wherein R in the above formula is 50 percent stearyl and 50 percent lauryl; a copolymer wherein R in the above formula comprises 50 percent lauryl and 50 percent octyl; also, a copolymer of 32 percent butyl methacrylate, 26 percent lauryl methacrylate, 34 percent stearyl methacrylate and 8 percent N-vinylpyrrolidone. Methacrylate polymers are usually employed in the form of a concentrate comprising approximately 20 to 50 percent polymer in a carrier oil. For synthetic lubricants it has been found advisable to use an ester-type carrier oil, such as dioctyl sebacate, trimethylolpropane tripelargonate or pentaerythritol tetracaproate. Methacrylate polymer concentrates can constitute 0.1 to 20 weight percent of the composition but are ordinarily used in a concentraion between 0.25 and 10 weight percent.

An anti-foam agent, such as a hydrocarbon or kerosene concentrate of a dialkyl silicone, can be advantageously employed in the lubricant composition of the invention. Effective anti-foam agents include dimethyl silicone, diethyl silicone, dibutyl silicone and the like. The anti-foam agent is generally employed in an amount ranging from about 0.0001 to 0.01 percent by weight.

Detergents and dispersants may also be profitably employed in the lubricating oil composition of the invention. Suitable additives in these classes include the metal salts of the phenates and sulfonates.

Minor amounts of corrosion inhibitors, such as quinizarin, sebacic acid, alizarin, benzotriazole, purpurxanthrene, anthrarufin and chrysazin can be advantageously employed in the lubricating oil composition. In general, corrosion inhibitors of this type are effective in relatively small concentrations ranging from about 0.01 to 0.5 percent of the lubricant composition.

The lubricating composition of the invention was tested for its anti-corrosive, oxidation resistance and deposit inhibiting properties in the following tests: the 450 F. Anti-Oxidant Evaluation Test, the 425 F. Oxidation- Corrosion Test for 48 hours, the Oil Mist Deposit Test, the Stainless Steel Corrosion Test and the Erdco Bearing Tests.

The 425" F. Oxidation and Corrosion Test is conducted in accordance with Method 5308.4 of Federal Test Method and Standard No. 791a (issued Dec. 31, 1961) except for the following modifications to conform to Pratt & Whitney Aircraft Specification 52l-B (Type II). The bath temperature is maintained at 425 F.i1 F. instead of at 250 F. This test is conducted for a period of 48 hours instead of 168 hours, specified in the original test.

5 The 450 F. Antioxidant Evaluation Test is conducted by passing dry air at a flow rate of 30 liters per hour through the test sample in a glass test cell attached to a head suitable for collecting volatile oxidation products.

designated Acryloid A in the examples below. Run 1 is representative of the present invention. In all of the examples and claims below the additive concentration is in weight percent unless otherwise indicated.

TABLE I Run 1 Run 2 Run 3 Run 4 Inhibitor Components, wt. percent:

N-phenyl-0,0-dlphenylphosphoramidate 0. 5 0. 5 0. 5 0. 5 Dioctylphenothiazlne 0. 7 0. 7 0. 7 0. 7 Airline 1.4 0.6 0.6 1.0 Tests:

450 F. Anti-oxidant Test:

Percent Viscosity Increase:

t 24 hrs 55. 7 93. 2 i 193 60. At 48 hrs--- 339 619 503 TAN Increase:

t 24 hrs--. +2. 80 +4.03 +5. 24 +4. 31 At 48 hrs--- +5. 52 +8. 17 +8. 0 Deposits (gm 0. 4 0. 8 0. 3 0. 7 Sludge (percent) 0. 1 0. 1 0 l 2.0 425 F./48 Hr. Oxidation Corrosion Test: (PWA 521-B) Metal weights A in mgJcmfi: Cu- 0. 12 0. 06 0. 02 -0. 14 =0. 3 Fe- +0. 0 +0. 15 +0. 06 *0. 3 AL- +0. 06 -0. 07 0 +0. 04 =i=0. 3 Mg +0. 04 0. 06 -0. 06 +0. 09 0. 3 Ag--- +0. 11 +0. 03 0 ==0. 3 Ti +0.08 +0. 08 +0. 02 0 0. 3 Percent Viscosity Increas 20. 7 17. 0 40. 3 23. 4 +50 Max TAN Increase +2. 04 +1.49 +5. 02 2. 74 Oil Mist Deposits Test (600 F deposit/1,000

g. throughput 1. 07 l 2. 5

1 Dioctyldiphenylamine. 2 Diphenylamine. 9 Di-n-hexylamlne. 4 B1s(1,4-d.imethylpentyl)paraphenylene diamlne. 5 Fails test.

A steel specimen is immersed in the oil during the test. This test is run for 48 hours with determination of viscosity increase and total acid number taken at 24 hours and 48 hours.

The Oil Mist Deposits Test is conducted by passing a mist of oil through a glass tube containing a steel liner (shim stock) through the entire length of the tube. The tube is maintained at 600 F. while the oil mist is continuously passed through over a period of 16 hours. At the end of the test period, the steel liner is removed, solvent washed and weighed. The amount of tenacious material adhering to the liner is determined and is reported as grams of deposit per one thousand grams of oil put through the system. This test is representative of breather tube deposit formation in a jet engine. A description of this test has been published by the American Society of Lubrication Engineers (ASLE Paper No. 66LC-6).

A base oil which was employed in the preparation of lubricating oils tested below was a technical grade pentaerythritol esterified witha mixture of 38% valeric, 13% Z-methylpentanoic, 32% octanoic and 17% pelargonic acid. This base fluid designated Base Fluid A, had the following properties:

The tests set out in Table I above show that there is specificity in the amine component of lubricating oil composition of the invention. The lubricating oils of Runs 1 through 4 are identical except for the amine component. In addition to the inhibitor components indicated, the lubricating oil compositions of Runs 1 through 4 consisted of 0.1% quinizarin, 0.3% Acryloid Additive and the balance Base Fluid A described above. The Acryloid Additive is a commercially available viscosity index improver consisting of a solution of Acryloid polymers in di-Z-ethylhexyl sebacate. The Acryloid polymer is a copolymer of 90% mixed methacrylic esters ranging from butyl to stearyl polymerized with 10% of an unsaturated nitrogenous compound. This V.I. impr'over is Due to the complex requirements which must be met by a synthetic aircraft turbine oil and the fact that these requirements are constantly becoming more severe with the rapid advances in engine, technology, there are no universally accepted criteria for all the properties of such a lubricating oil. It is essential for the lubricant manufacturer to set high performance standards for all the properties of the oil in order to formulate an effective product. In addition to the requirements of the Pratt & Whitney Aircraft corrosion specifications (PWA 521-B), the oils of this invention meet high anti-oxidant and deposits standards as shown by Run 1 in Table I above. Run 2 failed on the basis of excessively high Oil Mist Deposits. Run 3 failed because of the excessive viscosity increase of 193% in 24 hours and Run 4 failed because of the excessive 2.0% sludges in the anti-oxidant test.

Runs 5 through 9 in Table II below show the effectiveness of various base oils and different phosphoramidates.

Base Fluid B was a technical grade pentaerythritol esterified with a mixture or 20% 2-methylpentanoic acid, 50% valeric acid and 30% pelargonic acid.

Base Fluid C was a trimethylolpropane esterified with a mixture of 1% valeric, 8% hexanoic, 13% heptanoic, 5% octanoic, and 73% pelargonic acids.

Base Fluid D was trirnethylolpropane tris(neoheptanoate).

The Acryloid Additive is the same as that described above.

Additive A is a load-carrying additive consisting of a 49 weight percent solution of the monoamide of 2-aminopyridine and trimer acid in the pentaerythritol tetraester described above as Base Fluid A. The monoamide is prepared by direct condensation of Z-aminopyridine (0.33 equivalent) and the trimer of unsaturated C fatty acids (1.0 equivalent based on Saponification Number) at 350-400 F. for approximately 8 hours followed by removal of the water of reaction by azeotropic distillation. Additive A is eifective in a concentration ranging from about 0.05 to 0.5 percent.

The anti-foam additive was a 10 percent solution of dimethyl silicone in kerosene and the solution was employed in a concentration of 50 parts of solution per million of the lubricating oil.

TABLE II Run Run 6 Run 7 Run 8 Run 9 Composition, wt. percent:

Base Fluid B C D A A Quinizarln..- 0. 0.10 0. 10 0. 10 0.10 Acryloid A 0.30 0.30 0.30 0.30 0. 30 N-phenyl-0,0-diphenylphospboramidate 0. 50 0.50 N-phenyl-0,0bis(nonylphenyl) phosphoramidate 1.00 1.00 1. 00 Dioctylphenothiazine 0. 70 0. 70 0. 7 0. 70 0.70 Dioctyldlphenylamine 1. 40 1. 40 1. 40 1. 40 1. 40 Additive A 0. 16 0.16 0.16 0.16 0. 16 Dimethyl silicone s0ln., p.p. 50 50 50 50 50 Tests:

450 F. AOST:

Percent Viscosity Inerease' At 24 hrs- 55.6 48. 8 11.6 46 61 367 292 44 293 366 2. 8O 4. 88 0.43 2. 26 3.6 8. 44 9.14 1. 37 7. 42 7. 9 0. 5 0. 6 0. 4 0. 2 0. 3 Sludge, percent. Trace Trace 0. 1 0. 1 Trace 425 F./48 Hr. 0xid.-Corr. Test: (PWA 521-13) Corn, mgJcmfi: Cu 0. 25 0. 0. 39 0. 14 0. 17 0. 3 +0.04 +0.02 +0.03 0 0 =03 +0.06 +0.03 +0.05 0. 04 0. 04 *0. 3 +0. 04 +0.03 +0. 04 0. 04 0. 3 0 0. 07 0 0 ==0. 3 Ti +0. 03 +0.03 0 0. 07 0 0. Percent Visconsity Increase. 24 22 22. 3 25. 5 +50 Max. TAN Increase 4. 71 6. 21 5. 2. 8 3. Oil Mist Deposit Test (600 F.), g. de-

posit/1,000 g. throughput 0. 4 1. 5 0. 9 0.2 0.9

The foregoing Runs 5 through 9 show that acceptable synthetic lubricating oil compositions can be prepared from esters of pentaerythritol and trimethylolpropane and that a variety of phosphoramidates are effective.

Runs 10 through 13 in Table III below give comparison data for two turbine oils of the invention, a commercial product, and an oil representative of a second commercial product. The oil used in Run 10 is a synthetic aircraft turbine oil in commercial use having the same base fluid as the preferred lubricating oils of the invention, namely Base Fluid A described above. The inhibitor package of this oil is based upon phenothiazine and dioctyldiphenylamine. The lubricating oils in Runs 11 and 12 are identical except for the phosphoramidate component. These oils consisted of 1.4% dioctyldiphenylamine, 0.7% 'dioctylphenothiazine, 0.3% Acryloid A, 0.16% Additive A, 0.1% quinizarin, p.p.n1. dimethyl silicone solution plus a phosphoramidate in Base Fluid A. Runs 11 and 12 are representative of the present invention. The oil used in Run 13 is representative of a second type of synthetic aircraft turbine oil in commercial use. It has the same Base Fluid A but employs an inhibitor package based upon phenyl-a-naphthylamine and dioctyldiphenylamine.

It can be seen from the foregoing data that the commercial oil of Run 10 is extremely corrosive to stainless steel as compared to the oils of Runs 11, 12 and 13. The oils of Runs 11 and 12 of the invention are far superior to the commercial oils of Runs 10 and 13 in Demerit Rating in the Erdco Bearing Test under Type 1.5 and Type 2 conditions. The Type 2.5 and Type 3 Erdco Bearing Test data compare an oil of this invention (Run 11) with a current commercial synthetic lubricant (Run 10) under test conditions which are used to evaluate the operating capability of lubricants under more severe conditions such as will be encountered in the supersonic transport (SST). The commercial lubricant required three oil changes to complete 100 hours under the Type 2.5 test conditions (550 F. bearing temperature, 450 F. oil in temperature and 490 F. bulk oiil temperature), whereas the oil of this invention essentially completed this test with one oil change while causing very little deposit formation. The oil of this invention successfully completed a Type 3 test (600 F. bearing temperature, 500 F. oil in temperature and 540 F. bulk oil temperature) with three oil changes, which was similar to those of the commercial oil under the more moderate Type 2.5 test conditions. Thus the oil TABLE III Run 10 Run 11 Run 12 Run 13 Test Limits Composition, wt. percent: Phosphoramidate Tests:

410 Stainless Steel Corrosion, 550

F./ hr.,mg 658 6 5 2 Anti-Oxidant Test (450 F./48 hr.):

Percent Vis. Inc 550 203 306 700 TAN Inc 7. 9 7. 4 7. 9 9.0 MIIrL23GO0A Erdco Bearing Test, Type 1.5:

Demerit Rating-...- 74 14 16 30 Max. Percent Vis. Inc (100 F 18 18 17 18 5 to 25 TAN Inc 1. 1 1. 4 1. 4 1. 9 2.0 Max. PWA 521-3 Erdco Bearing Test, Type 2:

Demerit Rating 72 30 33 72 (Pass) Percent Vis Inc 1,436 167 192 181 Inc 6.7 4.3 5.2 4.0 Erdco Bearing Test, Type 2.5:

Demerit Rating 178 (100 Hrs.) 67 Hrs Hours to Oil Change 43 80 Percent Vis. Inc. (100 F.) 291 265 75 352 TAN Inc 3.4 4.7 2.2 4.4 Erdco Bearing Test, Type 3:

Demerit Rating 141 (100 Hrs.) Hours to Oil Change 43 88 100 Percent Vis. Inc. (100 F.)... 377 842 44 'IAN Inc 2.5 3.1 1.3

1 0.5% N-phenyl-0,0-diphenyl phosphoramidate. i 1.0% N-phenyl-0,0'-bis(nonylpheny1) phosphoramidate.

of this invention demonstrates a 50 F. operating temperature improvement over the commercial synthetic turbine oil lubricant.

In Table IV below, lubricating oils of the invention, Runs 14 and 15, are compared to similar lubricating oil compositions in which one or more of the critical inhibitor components, namely the alkylated phenothiazine, alkylated diphenylamine or phosphoramidate has been omitted from the composition. The base oil employed in Runs 14 through 22 was Base Fluid A described above. In addition to the inhibitor package indicated for each Run and Base Fluid A, all of the lubricating oil compositions contained Acryloid A, 0.16% of Additive A described above, 0.10% quinizarin and 50 p.p.m. of dimethyl silicone fluid.

4. A composition according to claim 1 in which said alkylated amine is dioctyldiphenylamine and said alkylated phenothiazine is dioctylphenothiazine.

5. A synthetic lubricating oil composition according to claim 1 containing from 0.2 to 2 percent of said phosphoramidate from 0.7 to 2.5 percent of said alkylated amine and from 0.3 to 1 percent of said alkylated phenothiazine.

6. A synthetic lubricating oil composition according to claim 1 in which said ester-base fluid is a tetraester of pentaerythritol.

7. A synthetic lubricating oil composition according to claim 1 in which said phosphoramidate is N-phenyl-0,0- bis (nonylphenyl) phosphoramidate, said alkylated amine is dioctyldiphenylamine and said alkylated phenothiazine is dioctylphenothiazine.

Anti-oxidant, Test (450 F.)

24 Hr. Data 48 Hr. Data Percent Percent Dioctyl- Dioctyl- Percent Percent Centrifuge phenothiadiphenyl- Vis. TAN Vis. Inc. TAN Sludge Sludge, Run zine amine Percent Phosphoramidate Inc. Inc. (100 F.) Inc. (g.) percent 0.7 1.4 0.5 N-pheny1-0,0-diphenyl phosphoramidate.. 56 3.4 349 10.4 0.5 Trace 0. 7 1.4 1.0 Nt-iplgenyl-o,O-bis(nonylphenyl) phosphor- 55 5. 3 406 11. 2 0. 5 0. 1

arm a e. 1. 4 1. 4 185 5. 3 2, 240 12. 0 0.6 0.2 1. 4 1. 4 192 4. 6 1, 980 6. 4 0. 7 0. 2 1. 0 1.0 Nphenyl-0,0-bis(nonylphenyl) phosphor- 241 6. 5 2, 799 11.9 1.1 0. 1

amt a e. 2. 0 "do 187 5. 3 1, 847 12. 2 1. 1 0. 1 1.4 0.5 N-phenyl-0,0-diphenylphosphoramidate. 238 6.0 1. 760 11.1 1. 0 0. 1 21 2.0 ...do 171 5. 3 1, 160 10.0 0. 6 0.1 22 4.0 N-phenyl-0,0-bis(nonylphenyl) phosphor- 470 5.5 0. 6 Trace amidate. (24 hr.) (24 hr 23 Base F1uid-no additives 688 5. 9 Solid 0. 2 1. 3 Trace It is apparent from the tests in Table IV that the omission of any one of the inhibitors, alkylated phenothiazine, alkylated diphenylamine or phosphoramidate results in a lubricating oil which is very poor in the Anti-Oxidant Evaluation Test. This is shown in the extraordinary viscosity increases for all of the lubricants in Runs 16 through 22.

The foregoing tests demonstrate the unusual oxidation and corrosion resistance and deposit cleanliness of the synthetic lubricating oil composition of the invention. The performance of the lubricant in the extremely severe Erdco Bearing Tests Type 2.5 and Type 3 demonstrates the effectiveness of this lubricant under more severe conditions than expected in the next generation of jet engines.

Obviously many modifications and variations of the invention, as hereinafter set forth, may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A synthetic lubricating oil composition comprising a major portion of an aliphatic ester base oil having lubricating properties formed from the reaction of a pentaerythritol or trimethylolpropane and an organic acid having from about 2 to about 12 carbon atoms, containing from about 0.1 to 4 percent of a phosphoramidate having the formula:

in which R is an aryl or alkaryl radical having from 6 to carbon atoms and R and R each represent a hydrocarbyl radical having from 4 to 20 carbon atoms, from 0.5 to 4 percent of an alkylated diphenylamine in which the alkyl radicals have from 4 to 20 carbon atoms, and from 0.1 to 3 percent of an alkylated phenothiazine in which the alkyl radicals have from 4 to 20 carbon atoms.

2. A synthetic lubricating oil composition according to claim 1 in which said phosphoramidate is N-pheny1-0,0'- bis (nonylphenyl) phosphoramidate.

3. A synthetic lubricating oil composition according to claim 1 in which said phosphoramidate is N-pheny1-0,0'- diphenyl phosphoramidate.

8. A synthetic lubricating oil composition according to claim 1 in which R, R and R" each represent a phenyl or alkylphenyl radical.

9. A synthetic lubricating oil composition according to claim 5, which also contains from 0.25 to 10% of a methacrylate polymer and from 0.01 to 0.5% of quinizarin.

10. A synthetic lubricating oil composition according to claim 5 containing from 0.01 to 0.5 percent of quinizarin and from about 0.05 to 0.5 percent of the monoamide of 2-aminopyridine.

11. A synthetic lubricating oil composition according to claim 1 in which said ester-base fluid is trimethylolpropane esterified with a mixture of 1% valeric, 8% hexanoic, 13% heptanoic, 5% octanoic and 73% pelargonic acids.

12. A synthetic lubricating oil composition according to claim 1 in which said alkylated phenothiazine has the formula:

in which R is an alkyl radical having from 4 to 2-0 carbon atoms and R is hydrogen or an alkyl radical having from 4 to 20 carbon atoms.

13. A synthetic lubricating oil composition according to claim 12 in which R is an octyl radical and R is hydrogen.

References Cited UNITED STATES PATENTS 3,236,774 2/1966 Thompson et al. 25256 X 3,247,111 4/ 1966 Oberright 25234.7 3,256,196 6/1966 Eickemeyer et a1. 25251.5 3,282,971 11/1966 Metro et a1 25256 X 3,309,317 3/ 1967 Wittner et a1. 25249.9

DANIEL E. WYMAN, Primary Examiner W. CANNON, Assistant Examiner US. Cl. X.R. 

